On Siri's page about the Norwegian tanker THELMA it is written:
"Believed to have been shelled by the Italian submarine Marcello on Jan. 20-1941, 50N 18 45W, having lost touch with convoy HG 50. Thelma defended herself with her canon and arrived Oban on Jan. 25 undamaged."
Rohwer credits the Italian submarine MARCELLO (Teppati) with the sinking of the Belgian steamer PORTUGAL (1550 grt) in 50°N/19°W by gunfire at 12.20 hours on 20 Jan, 1941.
The PORTUGAL was reported missing on 20 January 1941 with all hands lost.
And according to this site about Italian submarines the attacker did not identify his target and it was even initially thought that the gun attack failed until long after the war:
Has anyone more informations about this incident?
I think its possible that Rohwer made a mistake in this case and that THELMA was the target of the Italian submarine. Remains the question what happened to PORTUGAL, but German aircraft were very active at this time. Does someone know claim lists for shipping sunk or damaged by the Luftwaffe in January 1941?